nonplussed
non-PLUSTadjMeaning so puzzled that one does not know what to say or do
Memory hook NON-PLUS: NO MORE to say. Ms. Ada asks Kai, “What is forever plus one?” He opens his mouth, closes it, and just stares, with nothing more to say. He is nonplussed.
When the parrot answered the phone, the caller was completely nonplussed.
In context The magician’s final trick left the audience nonplussed; no one could explain how the elephant had vanished from the stage, and for a moment nobody even clapped.
Similar baffled, bewildered, perplexed, puzzled
Opposite composed, self-possessed
From Latin non plus, “no more”: a point at which nothing more can be said or done.